1. Field of Invention
The present invention relates to an electric wire for automobile. More particularly, it relates to an electric wire for automobile which meets the demand for an improved tensile strength and a smaller diameter.
2. Description of Related Art
An automobile uses a wire harness, which is a bundle of many electric wires, for electric connection with electrical equipment. Some of electric wires used in a wire harness comprise conductors having a twisted wire structure, which is obtained by twisting a plurality of element wires. FIG. 1 shows a typical conductor (element wire aggregate) included in this type of wire. In FIG. 1, denoted at 1 is the conductor having a twisted wire structure in which six peripheral element wires 3 are arranged around a single central element wire 2 like a single circle in tight adherence with each other and twisted. So far, in general, copper or copper alloy has been used as the central element wire 2 and the peripheral element wires 3 which form the conductor in such a twisted wire structure. Further, the diameters of the central element wire 2 and the peripheral element wires 3 are customarily the same. As a further general aspect, the nominal cross sectional area of the conductor is approximately 0.35 mm2 for use within a car room and approximately 0.50 mm2 for use within an engine room.
Meanwhile, the recent years have seen an increasing demand to an electric wire for automobile for an improved tensile strength and a smaller diameter. However, in the case of the electric wire shown in FIG. 1, it is necessary to increase the diameter of the conductor to improve in tensile strength, which contradicts the demand for a smaller diameter.
In light of this, an object of the present invention is to provide an electric wire for automobile which realizes a better tensile strength when the diameter of a conductor remains unchanged, maintains a tensile strength comparable to that of a conventional electric wire for automobile even when the diameter of the conductor is reduced, and achieves an equally favorable or better tensile strength than that of a conventional electric wire for automobile depending upon how thin the diameter of the conductor has been reduced.
As a result of intensive researches, it is possible to improve a tensile strength when stainless steel is used as a central element wire, and with an appropriate relationship satisfied between the cross sectional area of the central element wire and that of a conductor, it is possible to meet the demand for a smaller diameter which has been met almost to a limit and nevertheless ensure a tensile strength while preventing bending fracture.
Furthermore, when the diameter of the central element wire is made larger than the diameters of peripheral element wires, a compressed conductor is used as the conductor and the compression rate from the cross sectional area of the compressed conductor before compression to the cross sectional area after compression is within a proper range, it is possible to better meet the demand for a smaller diameter, solve the problem of heat generation as the peripheral element wires break before the central element wire does, and maintain an excellent impact breaking load.